An automotive reflective mirror element such as that which is part of an automotive rearview assembly often has to be heated during a cold season in order to defrost the surface of the mirror element. With most such mirror elements, an electrical heating element is arranged adjacent to a back surface of the mirror. Existing automotive mirror heating technologies relying on resistive heaters (such as constant-wattage, or CW, heaters and positive temperature coefficient, PTC, heaters) typically make use of a single heating element and one continuous heating circuit. As will be appreciated, conventional heaters used in vehicular rearview assemblies are deficient in several respects. Specifically, either of the abovementioned conventional heater tends to generate an output having a substantially uniform spatial profile that, considering asymmetry of shape and/or volume of an automotive mirror, results in a non-uniform heating profile across the mirror element. The resulting temperature gradients across the mirror produces stress in the glass of the mirror that can ultimately lead to glass fracture and mirror failure as a result of activation of a conventional defrosting heater. In addition, output power and power consumption characteristics of the CW and PTC heater designs are known to be subject to significant variations from part to part and from car to car. Prior attempts to create self-regulating automotive CW heaters have made use of mechanical thermostats, which are rather unreliable and even raise safety concerns due to overheating.